Currents at high and medium tension are commonly interrupted by means of circuit breakers in which the interruption chamber is filled with a dielectric gas such as sulfur hexafluoride (SF.sub.6).
At the moment the contacts open, the arc which develops between the contacts is subjected to a violent blast of compressed gas, thereby ensuring that the arc is extinguished at the next zero crossing of the current.
Such circuit breakers are expensive to construct because they must include means for compressing the blast gas and means for storing drive energy, sometimes in considerable quantities.
An aim of the invention is to provide a circuit breaker which does not require a gas compression device and which requires very low operating energy.
The interrupting principle used in the circuit breaker of the invention consists in establishing an arc tension which is greater than the network tension.
This principle is already used at low tension with air-filled current interrupting chambers. However the principle is not directly applicable to medium or high tension since the dielectric performance of air is inadequate and its deionization time constant is too long to allow a restoration voltage to develop, and the arc is restruck after each zero crossing of the current to be interrupted.
Attempts have therefore been made to use SF.sub.6 gas whose good dielectric performance and low deionization time constant should allow voltage to be restored easily after interrupting the current.
However, a difficulty arises in using SF.sub.6 due to the fact that arcing tensions in SF.sub.6 are much lower than arcing tensions in air and at medium and high tension it is difficult, (and industrially impossible) to create sufficient arcing tension in SF.sub.6 merely by stretching the arc.
This difficulty is solved by the present invention by using metal plates to split up the initial arc into a very high number of elementary arcs. The arcing tension of each elementary arc is due to voltage drops at the roots of the arcs and lies between 20 volts and 40 volts depending on the nature of the metal.
Another aim of the invention is to provide a medium or high tension current-limiting circuit breaker which opens automatically under the effect of a short-circuit current, thereby serving to limit the peak value of the short-circuit current to values which are equivalent to or less than the values obtained using current-limiting fuses.